A fuel cell system may be used to generate electric power for a variety of applications. Examples of these applications may include small household appliances to large industrial power plants that provide electric power to national power grids.
Fuel cell systems also vary in design and function. While all fuel cells generate electricity in an electro-chemical reaction that combines a fuel source and an oxidant source to release electrons, a particular system or method which provides the fuel and oxidant to the fuel cell electrodes and how the fuel and oxidant are combined may be quite different than another system. One such fuel cell system may utilize the compressor of a turbo-generator to pressure an oxidant (e.g., air), thereby creating a differential pressure between oxidant inlet and exhaust to force the oxidant to flow through a fuel cell system. Oxidant and fuel unused in the fuel cell electro-chemical reaction may be combined and burned to provide a high temperature and pressure fluid that may be expanded through a turbine. The energy extracted by the turbine may be used to power (rotate) the compressor. Turbine generated energy in excess of that required by the compressor may be used to power an electric generator. The electric power from this generator may be combined with the electric output of the fuel cell system. Additionally, the generator may be configured to operate as a motor that draws electric power to rotate the turbine and compressor of the turbo-generator.
The fuel cell, turbo-generator system described above may be useful in large scale fuel cell power plants that may provide power to a national power grid or other large scale electric power distribution system. A challenge for large scale electric power distribution systems is caused by the interaction of other power plants, power distribution equipment and power loads, all of which may affect the operating conditions of the electric power distribution system. If the operating conditions of the electric power distribution system are outside of safe operating limits for a fuel cell power plant tied thereto, the fuel cell power plant may need to be rapidly isolated from the electric power distribution system to prevent damage to the fuel cell power plant. However, the fuel cell electro-chemical reactions cannot be stopped as quickly as the fuel cell power plant can be disconnected from the electric power distribution system, thereby presenting a risk of internal damage to the fuel cell from the excess energy generated therein. Additionally, a fuel cell system may need to be cooled in a precise and controlled manner when shutting down (or heated when starting up) to prevent damage resulting from, e.g., uncontrolled oxidation of the fuel cell anodes. One method to control the cool-down rate of a fuel cell system may be to control the flow of the oxidant through the fuel cell. In a fuel cell power plant such as that as described above, these factors are complicated by the mechanical and electric interaction between the fuel cell system and the turbo-generator.
There remains a need for improved systems and methods that address the forgoing difficulties.
The present application discloses one or more of the features recited in the appended claims and/or the following features which, alone or in any combination, may comprise patentable subject matter.
In accordance with some embodiments of the present disclosure, an electric system is provided. The electric system may comprise a main AC bus, a transformer, switch gear, a fuel cell, a load bank, a turbine generator, a backup generator, an uninterruptible power supply (UPS) and a control system. The main AC bus may be electrically coupleable to an electrical power distribution system (EPDS) by the transformer and switch gear. The fuel cell may have a DC output bus that may be electrically coupled to the main AC bus by a fuel cell inverter. The load bank may be electrically coupled to the main AC bus. The turbine generator may have an AC output bus that is electrically coupled to the fuel cell DC output bus by a machine inverter. The backup generator may have an AC output bus electrically coupled to the main AC bus. The UPS may be electrically coupled to the main AC bus, and the control system electrically coupled to the UPS.
In accordance with some embodiments of the present disclosure, a method of operating a power plant having a fuel cell system and a turbine generator, each capable of providing power to an EPDS, is provided. If the power plant is connected to the EPDS, the method may comprises operating the fuel cell in a power generating mode to provide power to the EPDS, operating the turbine generator in a power generating mode to provide power to the EPDS or operating the turbine generator in a motoring mode wherein the generator draws power a fuel cell DC output bus, and operating a control system of the power plant by drawing power from a main AC bus of the power plant. If the power plant is disconnected from the EPDS, the fuel cell may be operated in power generating mode to provide power to the main AC bus and to the turbine generator if the turbine generator is operating in a motoring mode, the turbine generator may be operated in a power generating mode providing power to the main AC bus, the control system may be operated by drawing power from the main AC bus, and a load bank may draw power from the main AC bus.
In accordance with some embodiments of the present disclosure, a method of operating a power plant having a fuel cell and a turbine generator each capable of providing power to an EPDS is provided. If the fuel cell is not providing power to the EPDS and the power plant is connected to the EPDS, the turbine generator may be operated in a power generating mode to provide power to the EPDS or operated in a motoring mode wherein the turbine generator draws power from the EPDS, and the power plant control system may draw power from the main AC bus. If the fuel cell is not providing power and the power plant is disconnected from the EPDS, the turbine generator may be operated in a power generating mode and provide power to the main AC bus or operated in a motoring mode wherein the turbine generator draws power from the main AC bus, the backup generator may be operated to provide power to the main AC bus, the control system may be operated by drawing power from the main AC bus, and a load bank may be provided to draw power from the main AC bus if the turbine generator is operating in a power generating mode.
In accordance with some embodiments of the present disclosure, an electric system is provided. The system may comprise a main AC bus, a fuel cell having a DC output bus, a fuel cell inverter, a fuel cell load bank, a turbine generator having an AC output bus, a machine inverter, a grid inverter, a turbine generator load bank, a backup generator having an AC output bus, an UPS, and a control system. The main AC bus may be connectable to a utility grid by a transformer and switch gear. The fuel cell DC output bus may be connected to the main AC bus by the fuel cell inverter. The fuel cell load bank may be connected to the main AC bus. The turbine generator AC output bus may be connected to the main AC bus by a machine inverter and a grid inverter. The backup generator ac output bus may be connected to the main AC bus. The UPS may be connected to the main AC bus and may be configured to provide power to the control system. The system may further include a turbine generator load bank.
In accordance with some embodiments of the present disclosure, a method of operating a power plant having a fuel cell and a turbine generator, each capable of providing power to a utility grid, is provided. If the power plant is connected to the utility grid, the method may comprise operating the fuel cell in a power generating mode to provide power to the utility grid, operating the turbine generating in a power generating mode to provide power to the utility grid or operating the turbine generator in a motoring mode wherein the turbine generator draws power from the main AC bus, and operating a control system of the power plant by drawing power from the main AC bus. If the power plant is disconnected from the utility grid, the method may comprise operating the fuel cell in a power generating mode to provide power to the main AC bus, operating the turbine generator in a power generating mode to provide power to a turbine generator load bank, or operating the turbine generator in a motoring mode wherein power is drawn from the fuel cell, providing a turbine generator load bank that may draw power form the turbine generator, operating the control system by drawing power from the fuel cell, and providing a fuel cell load bank to draw power from the main AC bus.
In accordance with some embodiments of the present disclosure, a method of operating a power plant having a fuel cell and a turbine generator, each capable of providing power to utility grid, is provided. If the fuel cell is not providing power and the power plant is connected to the utility grid, the method may comprise operating the turbine generator in a power generating mode to provide power to the utility grid or operating the turbine generator in a motoring mode wherein the turbine generator draws power form the utility grid, and operating a control system of the power plant, wherein the control system draws power from the utility grid. If the fuel cell is not generating power and the power plant becomes disconnected from the utility grid, the method may comprise operating the turbine generator in a power generating mode to provide power to a turbine generator load bank, or operating the turbine generator in a motoring mode, wherein the turbine generator draws power from the backup generator, providing a turbine generator load bank to draw power from the turbine generator if it is oepratin in a power generating mode, operating the backup generator to provide power to the turbine generator if it is operating in a motoring mode, the backup generator also providing power to the control system, and operating the control system, the control system drawing power from the backup generator.
These and many other advantages of the present subject matter will be readily apparent to one skilled in the art to which the disclosure pertains from a perusal of the claims, the appended drawings, and the following detailed description of preferred embodiments.
While the present disclosure is susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and will be described in detail herein. It should be understood, however, that the present disclosure is not intended to be limited to the particular forms disclosed. Rather, the present disclosure is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure as defined by the appended claims.